Multiple choice

A and B can do a piece of work in 21 and 24 days, respectively. They start the work together and after some days A leaves the work and B alone completes the remaining work in 9 days. After how many days did A leave? A और B एक काम को क्रमशः 21 और 24 दिनों में पूरा कर सकते है। वे एक साथ काम शुरू करते है और कुछ दिनों के बाद A काम छोड़ देता है और शेष काम B अकेले 9 दिनों में पूरा करता है तो कितने दिनों बाद A ने काम छोड़ा?

  1. 5

  2. 6

  3. 7

  4. 8
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

A's work rate is 1/21 per day, B's is 1/24 per day. Together they do (1/21 + 1/24) = 15/168 per day. B worked alone for 9 days, completing 9/24 = 3/8 of the work. So 5/8 was done together, taking (5/8) / (15/168) = 7 days.

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